1. Field of the Invention
The present invention relates to a working method of a die for use for a Fresnel lens, a cutting tool for use with the working method, a die worked through the execution of the working method, and a Fresnel lens worked from the die.
2. Description of the Related Art
A Fresnel lens is the one that is obtained by repeatedly forming a lens surface having a fine width in the radial direction with the optical axis of the lens as a whole being set to be the center. This Fresnel lens is manufactured utilizing the die. As the dies there are a mother die having formed therein by cutting a number of Fresnel molding grooves each for forming a corresponding lens surface and a non-lens surface located between the adjacent lens surfaces, a master die molded from the mother die, and a stamper die molded from the master die. The master die is formed in such a way as to cause a transfer thereto of the Fresnel molded surface of the surface of the mother die having had formed therein a number of the Fresnel molded grooves. The stamper is formed in such a way as to cause a transfer thereto, again, of the Fresnel molded surface transferred to the surface of that master. Accordingly, the Fresnel molded surface of the surface of the stamper is complementary in configuration for the Fresnel surface of the Fresnel lens having formed therein the lens surface thereof. Onto the Fresnel molded surface of the stamper is caused to flow a molten state of UV-curable resin to a predetermined thickness. Then onto there ultraviolet rays are radiated to thereby cure the resin. Then the thus-cured resin is exfoliated from the stamper, whereby the Fresnel lens is formed.
The above-described mother die is formed into a predetermined configuration by performing cutting work based on the utilization of a diamond-made cutting tool as a cutting tool. However, because the blade end of the conventional cutting tool is formed sharpened, it sometimes happened that a chip-off of the tip occurred with the result that the service life of the cutting tool became short.
Thereupon, the present invention has an object to provide a working method which can prevent the decrease in the service life of the cutting tool due to the chip-off of it and a cutting tool for use with the working method. Another object of the present invention is to provide a working method and die that can add additional value to the Fresnel lens through the utilization of a technique for preventing the chip-off of the tip.
The present invention solves the above-described problems by the working method that will be mentioned below, etc.
The working method of the present invention is the one that is a working method of a die for use for a Fresnel lens, which is intended to work in an original die plate a Fresnel molding groove having wall surfaces corresponding to a lens surface and a non-lens surface of the Fresnel lens, wherein there is used a cutting tool in which one piece of edge line continuing to a blade end is constructed as a cutting edge; and the blade end has formed therein a notched portion which connects the one piece of edge line and another piece of edge line, whereby, while a relative rotating movement around a center line of the die is being made between the cutting tool and the original die plate, the cutting tool goes on to be fed into the original die plate with the cutting edge being used as the leading blade so that the wall surface corresponding to the non-lens surface of the Fresnel molding groove is gradually cut from an upper end thereof by the notched portion.
According to this working method, the notched portion is provided at the blade end of the cutting tool, and the wall surface corresponding to the non-lens surface is cut utilizing that notched portion. Therefore, the mechanical strength of the blade end increases with the result that the frequency at which the tip of the cutting tool gets chipped off decreases. It is thereby possible to prolong the service life of the cutting tool. Since the wall surface of the Fresnel molding groove is cut by the notched portion, it is possible to control the configuration properties such as the surface roughness, of that wall surface in conformity with the configuration of the notched portion. For example, it is possible to form by the notched portion a concavities/convexities configuration of cutting trace in the wall surface corresponding to the non-lens surface. In this case, a concavities/convexities portion resulting from the cutting trace is transferred to the non-lens surface of the Fresnel lens, with the result that the surface roughness of that non-lens surface becomes increased. Resultantly, the non-lens surface is constructed as a frosted-glass configuration of mat surface. Thus, the emission of stray light within the lens from the non-lens surface is suppressed with the result that the contrast is improved.
The cutting tool of the present invention is the one that is intended to work in an original die plate a Fresnel molding groove having wall surfaces which respectively correspond to a lens surface and a non-lens surface of a Fresnel lens, the cutting tool having a blade end and a pair of edge lines continuing to the blade end, whereby one piece of edge line is constructed as a cutting edge for cutting the wall surface corresponding to the lens surface of the Fresnel molding groove; and the blade end has provided therein a notched portion in such a way as to connect the one piece of edge line and another piece of edge line. According to this cutting tool, it is possible to realize the above-described working method.
The die of the present invention is the one that has a Fresnel molding groove which has been worked by the above-described working method. According to this die, it is possible to control the configuration properties of the wall surface corresponding to the non-lens surface by the notched portion of the cutting tool and thereby impart an optimum configuration to the non-lens surface of the Fresnel lens.
In the die of the present invention, in the wall surface corresponding to the non-lens surface of the Fresnel molding groove there may exist a concavities/convexities configuration of cutting trace which has been formed by the notched portion of the cutting tool having passed over that wall surface. If such is so done, it is possible to form the concavities/convexities portion corresponding to the manufactured based on the die to thereby increase the surface roughness of that non-lens surface.
The Fresnel lens of the present invention is the one that comprises lens surfaces and non-lens surfaces, wherein there is provided on at least one of no-lens surfaces a concavities/convexities portion based on a cutting trace which is formed at the time of working a die. According to this Fresnel lens, the non-lens surface is constructed as a frosted-glass configuration of mat surface. Thereby, the emission from the non-lens surface of stray light within the lens is suppressed with the result that the contrast is improved.